Purge systems are generally known and are used in different types of vehicles. Some types of turbo purge systems in vehicles equipped with turbocharging units use two check valves located remotely from a turbo purge valve to control turbo pressure and intake vacuum respectively to supply a source vacuum to a canister purge valve. The pressurized air generated by the turbocharger is forced into the engine to increase combustion pressure, and therefore increase the power generated by the engine. With some tubocharging systems, a portion of the pressurized air is bled off to create a vacuum and induce flow of purge vapor. The vacuum created is used as part of a purge system, where the purge system directs purge vapors from a fuel tank through various conduits to redirect the vapors into the intake manifold of the engine, and burn off these vapors through combustion.
The types of check valves used in these systems commonly check at very low vacuum pressure levels. Because these check valves check at such low vacuum pressure, it is difficult to use these valves to vent the fuel tank system and stabilize to atmospheric conditions prior to initiating the small leak test for on-board diagnostic (OBD) compliance.
To overcome this issue, these types of systems typically require a separate OBD relief valve to vent the fuel evaporative emissions (EVAP) system when the vehicle is shut off. The valve is necessary to conduct the OBD test. However, the inclusion of this valve adds complexity and cost to the system.
Accordingly, there exists a need for a valve assembly which is able to vent the fuel tank system, and allow the fuel tank system to stabilize to atmospheric conditions, as well as perform an OBD test, and control turbo pressure and intake vacuum pressure supplied to a turbo purge valve.